Sun
19
Apr
Beta-Carotene
Note:All the significant positive evidence for Beta-Carotene applies to food sources, not supplements.
Beta-Carotene belongs to a family of natural chemicals known as carotenes or carotenoids. Scientists have identified nearly 600 different carotenes. Widely found in plants, carotenes (along with another group of chemicals, the bioflavonoids) give color to fruits, vegetables, and other plants.
Beta-Carotene is a particularly important carotene from a nutritional standpoint, because the body easily transforms it to vitamin A. While vitamin A supplements themselves can be toxic when taken to excess, it is believed (although not proven) that the body will make only as much vitamin A out of Beta-Carotene as it needs. Assuming this is true, this built-in safety feature makes Beta-Carotene the best way to get your vitamin A.
Beta-Carotene is also often recommended for another reason: it is an antioxidant, like vitamin E and vitamin C. However, while high intake of carotenes from food has been associated with reduced risk of various illnesses (including heart disease and cancer), Beta-Carotene supplements have not been found to offer any benefits; in fact, when taken in high doses for a long period of time, Beta Carotene supplements might slightly increase the risk of heart disease and some forms of cancer.
Requirements
Although Beta-Carotene is not a required nutrient, vitamin A is essential for health, and Beta-Carotene is converted into vitamin A in the body. The exact conversion factor varies with the circumstances; in general, 2 mcg of Beta-Barotene in supplement form is thought to be equivalent to 1 mcg of vitamin A. See the article on vitamin A for requirements based on age and sex.
Dark green and orange-yellow vegetables are good sources of Beta-Carotene. These include carrots, sweet potatoes, squash, spinach, romaine lettuce, broccoli, apricots, and green peppers.
Dosages
We are not sure at the present time whether it is advisable to take dosages of Beta-Carotene supplements much higher than the recommended allowance for nutritional purposes, which is about 1.5 to 1.8 mg daily in adults. Rather than taking doses higher than this, it is probably much better to increase your intake of fresh fruits and vegetables.
Uses
There are no well-documented therapeutic uses of Beta-Carotene beyond supplying nutritional doses of vitamin A.
Numerous observational studies have found that a high intake of foods rich in carotenes is associated with a lower incidence of lung cancer, other forms of cancer and heart disease. However, beta carotene supplements have not been found to be helpful for preventing these conditions.
Similar evidence links high dietary intake of carotenes to a lower incidence and/or slowed progression of cataracts, macular degeneration and osteoarthritis but again there is no evidence that beta-carotene supplements are helpful for these conditions.
Preliminary evidence raised hopes that Beta-Carotene supplements might increase or preserve immune function or decrease symptoms among people with HIV. However, other studies found no benefit and some evidence hints that too much Beta-Carotene might actually be harmful.
Beta-Carotene supplements may be helpful for protecting the skin from sunburn, particularly in people with extreme sensitivity to the sun, but the evidence regarding this potential use is somewhat contradictory.
One preliminary study found evidence that beta-carotene might be helpful for cystic fibrosis, by helping prevent lung infections.
Beta-Carotene has been proposed as a treatment for alcoholism, asthma, depression, epilepsy, headaches, heartburn, male and female infertility, Parkinson's disease, psoriasis, rheumatoid arthritis, and schizophrenia, but there is little to no evidence that it works. There is some evidence that beta-carotene is not effective for cervical dysplasia and intermittent claudication.
Scientific Evidence
Cancer Prevention
The story of Beta-Carotene and cancer is full of contradictions. It starts in the early 1980s, when the cumulative results of many studies suggested that people who eat a lot of fruits and vegetables are significantly less likely to get cancer. A close look at the data pointed to carotenes as the active ingredients in fruits and vegetables. It appeared that a high intake of dietary carotene might significantly reduce the risk of lung cancer bladder cancer breast cancer esophageal cancer and stomach cancer
However, observational studies cannot prove cause and effect. It is always possible that individuals who consume a great deal of carotenes in the diet are different in other ways; for example, they might exercise more or have healthier lifestyles in other ways.
This is not a purely theoretical issue. For example, based primarily on observational studies, hormone replacement therapy was promoted as a heart-protective treatment for postmenopausal women. However, when placebo-controlled studies were performed, hormone replacement therapy was shown to slightly increase the risk of heart disease. One possible explanation for this discrepancy is that the apparent benefits of hormone replacement therapy were due to the fact that women who used it tended to belong to a higher socioeconomic class than those who did not. (For a variety of reasons, some of which are not known, higher income is associated with improved health.)
Something similar appears to be the case with beta-carotene. Although individuals who consume foods high in Beta-Carotene appear to obtain some protection from heart disease and cancer, when researchers gave Beta-Carotene supplements to study participants, there was no protective effect.
Most studies enrolled people in high-risk groups, such as smokers, because it is easier to see results when you look at people who are more likely to develop cancer to begin with.
The anticancer bubble burst for Beta-Carotene in 1994 when the results of the Alpha-Tocopherol, Beta-Carotene (ATBC) study became available. These results showed that Beta-Carotene supplements did not prevent lung cancer, but actually increased the risk of getting it by 18%. This trial had followed 29,133 male smokers in Finland who took supplements of about 50 IU of vitamin E (alpha-tocopherol), 20 mg of beta-carotene (more than 10 times the amount necessary to provide the daily requirement of vitamin A), both, or placebo daily for 5 to 8 years. (In contrast, vitamin E was found to reduce the risk of cancer, especially prostate cancer.)
In January 1996, researchers monitoring the Beta-Carotene and Retinol Efficacy Trial (CARET) confirmed the prior bad news with more of their own: The beta-carotene group had 46% more cases of lung cancer deaths. This study involved smokers, former smokers, and workers exposed to asbestos. Alarmed, the National Cancer Institute ended the $42 million CARET trial 21 months before it was planned to end.
At about the same time, the 12-year Physicians' Health Study of 22,000 male physicians was finding that 50 mg of beta-carotene (about 25 times the amount necessary to provide the daily requirement of vitamin A) taken every other day had no effect—good or bad—on the risk of cancer or heart disease. In this study, 11% of the participants were smokers and 39% were ex-smokers.
Similarly, another study of Beta-Carotene supplements failed to find any effect on the risk of cancer in women.
One possibility is that beta-carotene alone is not effective. The other carotenes found in fruits and vegetables may be more important for preventing cancer than Beta-Carotene. One researcher has suggested that taking Beta-Carotene supplements actually depletes the body of other beneficial carotenes.
It is also possible that intake of carotenes as such are unrelated to cancer, and that some unrelated factor common to individuals with a high carotene diet is the cause of the benefits seen in observational trials
Heart Disease Prevention
The situation with Beta-Carotene and heart disease is rather similar to that of Beta-Carotene and cancer. Numerous studies suggest that carotenes as a whole can reduce the risk of heart disease. However, isolated Beta-Carotene may not help prevent heart disease and could actually increase your risk.
The same double-blind intervention trial involving 29,133 Finnish male smokers (mentioned under the discussion of cancer and beta-carotene) found 11% more deaths from heart disease and 15 to 20% more strokes in those participants taking Beta-Crotene supplements.
Similar poor results with Beta-Carotene were seen in another large, double-blind study of smokers. Beta-carotene supplementation was also found to increase the incidence of angina in smokers.
Osteoarthritis
A high dietary intake of beta-carotene is associated with a significantly slower progression of osteoarthritis, according to a study in which researchers followed 640 individuals over a period of 8 to 10 years. However, as with heart disease and cancer, we don't know whether beta-carotene is responsible for this effect.
HIV Support
One small, double-blind study suggested that beta-carotene supplements might raise white blood cell count in people with HIV. However, two subsequent larger controlled trials found no significant differences between those taking Beta-Carotene or placebo in white blood cell count, CD4+ count, or other measures of immune function.
Evidence from observational studies suggests that higher intakes of vitamin A or beta-carotene may be helpful; however caution is in order regarding dosage. Researchers generally linked higher intake of vitamin A or Beta-Carotene to lower risk of AIDS and lower death rates, with an important exception: people with the highest intake of either nutrient (more than 11,179 IU per day of Beta-Carotene or more than 20,268 IU per day of vitamin A) did worse than those who took somewhat less.
Macular Degeneration and Cataracts
Despite promising results from observational studies, intervention trials of Beta-Carotene for these eye conditions have not shown benefit. Beta-Carotene proved ineffective for preventing cataracts in one large study and in another large study, Beta-carotene supplements combined with vitamin E and C failed to prevent either macular degeneration or cataracts.
Cervical Dysplasia
According to a 2-year, double-blind, placebo-controlled study of 141 women with mild cervical dysplasia (a pre-cancerous condition), beta-carotene, taken at a dosage of 30 mg daily along with 500 mg of vitamin C, does not help to reverse the dysplasia.38 Negative results were seen in other trials of beta-carotene as well.
Intermittent Claudication
A double-blind, placebo-controlled trial of 1,484 individuals with intermittent claudication found no benefit from Beta-Carotene (20 mg daily), vitamin E (50 mg daily), or a combination of the two.
The story of Beta-Carotene and cancer is full of contradictions. It starts in the early 1980s, when the cumulative results of many studies suggested that people who eat a lot of fruits and vegetables are significantly less likely to get cancer. A close look at the data pointed to carotenes as the active ingredients in fruits and vegetables. It appeared that a high intake of dietary carotene might significantly reduce the risk of lung cancer bladder cancer breast cancer esophageal cancer and stomach cancer
However, observational studies cannot prove cause and effect. It is always possible that individuals who consume a great deal of carotenes in the diet are different in other ways; for example, they might exercise more or have healthier lifestyles in other ways.
This is not a purely theoretical issue. For example, based primarily on observational studies, hormone replacement therapy was promoted as a heart-protective treatment for postmenopausal women. However, when placebo-controlled studies were performed, hormone replacement therapy was shown to slightly increase the risk of heart disease. One possible explanation for this discrepancy is that the apparent benefits of hormone replacement therapy were due to the fact that women who used it tended to belong to a higher socioeconomic class than those who did not. (For a variety of reasons, some of which are not known, higher income is associated with improved health.)
Something similar appears to be the case with beta-carotene. Although individuals who consume foods high in Beta-Carotene appear to obtain some protection from heart disease and cancer, when researchers gave Beta-Carotene supplements to study participants, there was no protective effect.
Most studies enrolled people in high-risk groups, such as smokers, because it is easier to see results when you look at people who are more likely to develop cancer to begin with.
The anticancer bubble burst for Beta-Carotene in 1994 when the results of the Alpha-Tocopherol, Beta-Carotene (ATBC) study became available. These results showed that Beta-Carotene supplements did not prevent lung cancer, but actually increased the risk of getting it by 18%. This trial had followed 29,133 male smokers in Finland who took supplements of about 50 IU of vitamin E (alpha-tocopherol), 20 mg of beta-carotene (more than 10 times the amount necessary to provide the daily requirement of vitamin A), both, or placebo daily for 5 to 8 years. (In contrast, vitamin E was found to reduce the risk of cancer, especially prostate cancer.)
In January 1996, researchers monitoring the Beta-Carotene and Retinol Efficacy Trial (CARET) confirmed the prior bad news with more of their own: The beta-carotene group had 46% more cases of lung cancer deaths. This study involved smokers, former smokers, and workers exposed to asbestos. Alarmed, the National Cancer Institute ended the $42 million CARET trial 21 months before it was planned to end.
At about the same time, the 12-year Physicians' Health Study of 22,000 male physicians was finding that 50 mg of beta-carotene (about 25 times the amount necessary to provide the daily requirement of vitamin A) taken every other day had no effect—good or bad—on the risk of cancer or heart disease. In this study, 11% of the participants were smokers and 39% were ex-smokers.
Similarly, another study of Beta-Carotene supplements failed to find any effect on the risk of cancer in women.
One possibility is that beta-carotene alone is not effective. The other carotenes found in fruits and vegetables may be more important for preventing cancer than Beta-Carotene. One researcher has suggested that taking Beta-Carotene supplements actually depletes the body of other beneficial carotenes.
It is also possible that intake of carotenes as such are unrelated to cancer, and that some unrelated factor common to individuals with a high carotene diet is the cause of the benefits seen in observational trials
Heart Disease Prevention
The situation with Beta-Carotene and heart disease is rather similar to that of Beta-Carotene and cancer. Numerous studies suggest that carotenes as a whole can reduce the risk of heart disease. However, isolated Beta-Carotene may not help prevent heart disease and could actually increase your risk.
The same double-blind intervention trial involving 29,133 Finnish male smokers (mentioned under the discussion of cancer and beta-carotene) found 11% more deaths from heart disease and 15 to 20% more strokes in those participants taking Beta-Crotene supplements.
Similar poor results with Beta-Carotene were seen in another large, double-blind study of smokers. Beta-carotene supplementation was also found to increase the incidence of angina in smokers.
Osteoarthritis
A high dietary intake of beta-carotene is associated with a significantly slower progression of osteoarthritis, according to a study in which researchers followed 640 individuals over a period of 8 to 10 years. However, as with heart disease and cancer, we don't know whether beta-carotene is responsible for this effect.
HIV Support
One small, double-blind study suggested that beta-carotene supplements might raise white blood cell count in people with HIV. However, two subsequent larger controlled trials found no significant differences between those taking Beta-Carotene or placebo in white blood cell count, CD4+ count, or other measures of immune function.
Evidence from observational studies suggests that higher intakes of vitamin A or beta-carotene may be helpful; however caution is in order regarding dosage. Researchers generally linked higher intake of vitamin A or Beta-Carotene to lower risk of AIDS and lower death rates, with an important exception: people with the highest intake of either nutrient (more than 11,179 IU per day of Beta-Carotene or more than 20,268 IU per day of vitamin A) did worse than those who took somewhat less.
Macular Degeneration and Cataracts
Despite promising results from observational studies, intervention trials of Beta-Carotene for these eye conditions have not shown benefit. Beta-Carotene proved ineffective for preventing cataracts in one large study and in another large study, Beta-carotene supplements combined with vitamin E and C failed to prevent either macular degeneration or cataracts.
Cervical Dysplasia
According to a 2-year, double-blind, placebo-controlled study of 141 women with mild cervical dysplasia (a pre-cancerous condition), beta-carotene, taken at a dosage of 30 mg daily along with 500 mg of vitamin C, does not help to reverse the dysplasia.38 Negative results were seen in other trials of beta-carotene as well.
Intermittent Claudication
A double-blind, placebo-controlled trial of 1,484 individuals with intermittent claudication found no benefit from Beta-Carotene (20 mg daily), vitamin E (50 mg daily), or a combination of the two.
Safety Issues
At recommended dosages, Beta-Carotene is believed to be very safe. The only side effects reported from Beta-Carotene overdose are diarrhea and a yellowish tinge to the hands and feet. These symptoms disappear once you stop taking Beta-Carotene or move to lower doses.
However, long-term use of Beta-Carotene supplements, especially at doses considerably above the amount necessary to supply adequate vitamin A, might slightly increase the risk of heart disease and certain forms of cancer.The solution: eat plenty of fresh fruits and vegetables, and get your Beta-Carotene that way.
In addition, some evidence suggests that Beta-Carotene supplements might cause alcoholic liver disease to develop more rapidly in individuals who abuse alcohol.